<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .btn{
            padding: 20px;
        }
    </style>
</head>
<body>
    <ul class="ul">
        <li class="li_1">li_1</li>
        <li class="li_2">li_2</li>
        <li class="li_3">li_3</li>
        <li class="li_4">li_4</li>
        <li class="li_5">li_5</li>
    </ul>
    <button class="btn">点我</button>

    <script src="../jquery/jquery.min.js"></script>
    <script>
        $('.ul').on('click', 'li', fun);

        function fun() {
            console.log(this);
            console.log(event.target);
            console.log(event.currentTarget);
            console.log($(this).text());
        }

        $('.ul').on('click', 'li', function () {
            console.log(this);
            console.log(event.target);
            console.log(event.currentTarget);
            $(this).css({
                backgroundColor: 'lightgreen'
            })
        })

        $('.btn').on('click', function () {
            // $('.ul').off()
            $('.ul').off('click', 'li', fun)
        })
    </script>
</body>
</html>